I spoke to IU, and they told me their oldest recent matriculant was a 51 yr old woman that started in 2001. However, she failed to graduate; they did not say why.

For what it’s worth, I did a little research and discovered that she matriculated with her daughter. So it was a bit of a news story at the time. She did not appear to have any ties to the University prior to her application. It looks like she was a high school math teacher at a small indiana town.